Background: Understanding the effects of cancer on the quality of life of affected patients is critical to clinical research as well as to optimal management and care. The aim of this study was to adapt the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire-C30 (EORTC QLQ-C30) questionnaire into Moroccan Arabic and to determine its psychometric properties. After translation, back translation and pretesting of the pre-final version, the translated version was submitted to a committee of professionals composed by oncologists and epidemiologists. The psychometric properties were tested in patients with cancer. Internal consistency was tested using Cronbach’s alpha and the test-retest reliability using interclass correlation coefficients. Construct validity was assessed by examining item-convergent and divergent validity. It was also tested using Spearman’s correlation between QLQ-C30 scales and EQ-5D. Results: The study was conducted in 125 patients. The Moroccan version was internally reliable, Cronbach’s α was 0.87 for the total scale and ranged from 0.34 to 0.97 for the subscales. The intraclass correlation coefficient of the test-retest reliability ranged from 0.64 for “social functioning” to 0.89 for “physical activities” subscales. The instrument demonstrated a good construct and concomitant validity. Conclusions: We have developed a semantically equivalent translation with cultural adaptation of EORTC QLQ-C30 questionnaire. The assessment of its measurement properties showed that it is quite reliable and a valid measure of the effect of cancer on the quality of life in Moroccan patients.